feat: Visual CoPilot module + collapsible sidebar

- Add visual-copilot module (iframe embed, env: NEXT_PUBLIC_VIM_URL)
- Sidebar collapse to icon-only with localStorage persistence
- Tooltips on collapsed nav items
- Full-viewport layout for canvas routes (/visual-copilot)
- Register module in modules.ts + feature flag in flags.ts

src/app/(modules)/visual-copilot/page.tsx

@@ -0,0 +1,5 @@
+import { VisualCopilotModule } from "@/modules/visual-copilot";
+
+export default function VisualCopilotPage() {
+  return <VisualCopilotModule />;
+}